1. Field of the Invention
The present invention relates to a device for introducing light that is emitted from a light source lamp to an illuminating light guide fiber bundle of an endoscope.
Generally, the incident end faces of light guide fiber bundles of endoscopes have an exceedingly small area. It is therefore necessary to condense light that is emitted from a light source lamp into a small spot of light and to dispose the incident end face of a light guide fiber bundle at a point where the light is converged so that the quantity of light that enters the light guide fiber bundle is maximized.
However, it is difficult to converge the illuminating light on the incident end face of the light guide fiber bundle in complete spot-like form because the light source lamp has a certain size of its own.
2. Description of the Prior Art
FIG. 4 shows a conventional illuminating light introducing device, in which a convex lens 51 is disposed in close proximity to an incident end face 52c of a light guide fiber bundle 52 with a view to maximizing the quantity of light that enters the light guide fiber bundle 52.
In the conventional illuminating light introducing device, however, the one of the two surfaces 51a and 51b of the convex lens 51 that faces the incident end face 52c of the light guide fiber bundle 52, i.e., the surface 51b, is a planar surface and consequently the light that is refracted by the convex surface 51a enters each of the optical fibers comprising the light guide fiber bundle 52 at a large angle of incidence.
As a result, the illuminating light is reflected an exceedingly large number of times inside each of a multiplicity of optical fibers 152 comprising the light guide fiber bundle 52, as shown in FIG. 5. Accordingly, the transmitted light is gradually attenuated as it is repeatedly reflected, resulting in a marked reduction in the quantity of illuminating light that is applied to an object of observation.